Such electrical cable trays are most useful in power plants and other buildings to organize the cables throughout the plant, and in other applications where overhead ceiling support of cables is required, or in building partitions, and for anchoring in brick faces of buildings and the like. The right-angular and other joining of open U-shaped channels for constructing the ladder-like or other skeletal support structure for such trays and the like is principally effected with aid of stud bolts generally having hexagonal ("hex") heads that enable the installer to tighten the same where, for example, right-angular position clamping plates are to secure right-angularly oriented channels together, as later more fully described in connection with the drawings of this application and in current bulletin sheets of Unistrut House of Bedford, England, entitled "Unistrut Building Systems" and "Metal Framing Structures".
In use, the installer manually tightens the hex head bolt that passes through the channel clamping plate into the spring-held nut inserted within the channel, and determines by "feel" and experience the proper tightness of the bolt. A major problem with such assembly techniques, however, resides in the fact that if the bolt is tightened too much, it can cause the edge lips of the channel, against which the nut bears, to collapse, such that the channel loses its structural integrity. If, on the other hand, the installer fails to tighten the bolt quite enough, the channel members being fastened together can slip or slide relative to one another, causing structural and safety problems.
While particularly in other applications, bolts with splined tips have been proposed to shear when a predetermined bolt tightening or tension is reached, such as, for example, of the type described in U.S. Pat. No. 3,812,757 and in the current catalogue of the assignee herein, entitled "TCB Features of High Strength TCB Bolts", for the purposes of the present invention, taking the responsibility of determining appropriate bolt tighteners totally out of the hands of the installer is most important; and concomitant with the same, techniques for reliably pre-setting and calibrating the precise degree of tightening inherently in the bolt structure, and parts location adapted to permit ready visual external inspection of proper tightening, and with a minimum number of parts in the bolt-nut assembly, are important.